PITTSBURGH — The Rangers were hit with some sad news late Thursday, finding out that the mother of forward Martin St. Louis died unexpectedly in the afternoon.

The team confirmed her passing, yet the availability of St. Louis for Friday night’s Game 5 against the Penguins at Consol Energy Center was unknown.

France St. Louis was 63.

It was a gripping bit of honesty, something it seems Alain Vigneault had been dancing around saying for the entirety of these playoffs.

But with the Rangers on the brink of elimination, down 3-1 in this best-of-seven series and facing a must-win Game 5, the coach said what everybody had been thinking concerning his No. 1 defenseman, Ryan McDonagh.

“Ryan hasn’t had — and he’ll be the first to say it — the playoffs to his expectations and to ours,” Vigneault said. “He has an opportunity [Friday] to change that, but obviously he hasn’t played very well.”

McDonagh was far-and-away the team’s best defenseman during the regular season, surely garnering more than a handful of votes for the Norris Trophy. Yet he injured his left shoulder in a game in Vancouver on April 1, and missed the final five games of the regular season.

He hasn’t missed a game in the playoffs, and repeatedly has said he has no physical restrictions.

Vigneault didn’t have speedy winger Carl Hagelin on the ice for a full-team, hour-long practice on Thursday, the only player on the team given a “maintenance day.” In his absence, the forward lines were different, and that brought up the possibility of some things changing for this do-or-die Game 5.

“We’re looking at all possibilities right now,” Vigneault said. “We’ve had a fair amount of success by being consistent.”

The most consistency up front had come from the line of Benoit Pouliot-Derick Brassard-Mats Zuccarello, yet in practice, Zuccarello was replaced by the struggling Martin St. Louis, while Zuccarello took St. Louis’ spot next to Chris Kreider and Derek Stepan.

“We’re looking for a solution,” Brassard said. “If we break up our line, it doesn’t matter. We just have to find something that is going to work.”

Kreider played his first game of the 2014 playoffs on Wednesday, having missed the previous 19 with a fracture in his left hand, and Vigneault didn’t hesitate to be critical in his assessment of Kreider’s performance.

“I saw a young man that worked extremely hard and wanted it real bad,” Vigneault said. “Obviously, timing-wise with the puck, and decision-wise with the puck, he fit in real great with our group — meaning, he was off.”

Another wrinkle at practice was defenseman John Moore was back with Kevin Klein on the third pair. Raphael Diaz had been in that spot for the past two games in place of Moore, but Diaz instead skated with unequivocal-scratch Justin Falk.